X-ray spectrograph



g; 1963 J. LADELL ETAL 02,196

X-RAY SPECTROGRAPH Filed NOV. 25, 1959 5U/PF/7CE PARALLEL 7'0 403 Pun/E INVENTORS. eEsHUA LADELL BY NATHAN SPIELBERG A6EN..

X-RAY SPECTROGRAPH p Joshua Ladell, Flushing, and Nathan Spielberg, Hartsdale, N.Y., assignors to North American Philips Company, Inc., New York, N.Y., a corporation of Delaware Filed Nov. 23, 1959, Ser. No. 854,674' 7 i 6 Claims. (Cl.-250-51.5)

adapted for use with a micro-probe X-ray analyzer.

More particularly, in the instrument described in thatapplication, a specimen of thematerial is excited to produce characteristic X-rays of each of the elements in the material. Since each element emits characteristic X-rays which have different wave-lengths, a .diifracting crystal which has been cut to dilfract radiation of each of a pluralit'yof wave-lengths at angles determined by the recip rocal lattice construction of the crystal is positioned to intercept these characteristic X-rays and reflect the several Wave-lengths simultaneously at different angles toward detcctors pointed at the diifracting crystal which detect a wave-length corresponding to that of one of the elements,

United States Patent ceiving slits and associated detectors placed at thesepositions permit simultaneous recording of all Wave-lengths. 1

A principal object of the present invention isto increase the sensitivity of such an instrument.

Another object of the invention is to obtain a higher intensity of the characteristic X-rays from a smaller source.

A further objectof our invention is toreduce the background and scattering effects by utilizing receiving slits and detectors of smaller cross-section,

, Another object of our invention is to simplify the shielding required with such'instruments.

These and further objects of the invention will appear as the specification progresses. y

In accordance with our invention we employ a crystal which not only reflects the different wave-lengths corresponding to each of the elements at difierent angles thereby permitting simultaneous detection of several wavelengths, but also one which focusses each of the wavelengths .at a series of points conveniently located on a circle, hereinafter referred to as the focussing circle.

Thus, in accordance with our invention, we employ a crystal Which not only satisfies the general conditions specified in the aforesaid copending application, i.e., a crystal which has been prepared to reflect each wavelength at an angledetermined by the reciprocal lattice construction of the crystal, but is also deformed into a curved surface so as to converge each of these wavelengths at a point on the focusing circle. The deformation may either be plastic or elasticvor both. For elastic crystals, the crystal is bent and mechanically constrained to maintain the desired curvature. Plastically deform able crystals appropriately shaped may also be used. Consequently, if the detectors are positioned at points on the circleat which the respective wave-lengths are focussed, the intensity of the detected radiation will be greater than if a flat crystal is used which does not focus the radiation. D

The crystal We employ is a modified focussing crystal monochromator, i.e., a crystal whichhas been prepared to reflect each wave-length at an angle determined by the reciprocal lattice construction of the crystal. The reciptice.

through the reciprocal lattice origin.

. 3,102,196 Patented Aug, 27, 1963 p 2 rocal latticeis a three-dimensional network of points throughout space surrounding each unit cell of the crystal. Each point in the reciprocal lattice is separated from the origin of the reciprocal lattice by adistance inversely proportional to the interplanar spacing of the crystal planes that it represents, and its direction from the origin is exactly the same as the direction of the normal to the planes (cf., X-ray Crystallography, M. I. Buerger, chapter 6, p. 107, et seq., for a more complete discussion of the reciprocal lattice). t

The crystal monochromator itself maybe of the Johansson-Du Mond type, or of the Johann, Cauchois or logarithmicspiral type. In one embodiment illustrated, we employ a quartz crystal with a surface initially parallel to the planes which then bent tocylin drical shapeof radius 2R, with the axis of the cylinder parallel to the b-. axis of the crystal and the surface ground to a oylindercf radius R (again with axis parallel to 17). Radiation from a narrow source, i.e., a point or line sourcegor a' source slit placed on the. focussing circle (radius R) is diffracted by the crystal and refoc'cussed, again on the focussing circle, depending upon the wave-length involved, and. re-

The invention will be described with reference to th accompanying drawing in which: i

FIG. 1 shows a spectrograph according to the inven tion employing a reflecting or Johansson-Du Mond type of crystal monochromator; and FIG. 2 shows another embodiment of the invention employing a transmission or surrounded by shield v14, emitssecOndaIy X-rays whose wave-lengths are characteristic of each of the elements in the specimen. Alternatively, the specimen could be exposed to a focussed beam of electrons of sufficient energy to produce characteristic X-rays from elements in the specimen. The cone 4 of characteristic X-rays from the specimen is limited by a slit 5 and intercepted by a diffractin-g crystal monochromator 6 Whose reflecting surface 7 is ground to a cylinder of radius R so that it forms an arc of the focussing circle. A plurality of detectors 8, 9, 10, 11 and 12 are positioned at various points around the focussing circle and are pointed toward the dilfracting crystal to intercept cones of X-rays focused at those points by a crystal rnonochromator. 1

As described in copending application Serial N o.'771,- 621, now US. Patent 3,046,399, the crystal is, oriented to simultaneously difiract N wave-length into N detectors 3 positioned at various angles with respect to the crystal. The prinicple used to cause simultaneous diffraction into N detectors is governed by satisfying the Lane condition for N characteristic radiations land at least N sets of crystallographic planes (hkl), The simultaneous diffraction from N planes (hkl) corresponding to N characteristic radiations M is accomplished by orienting especially cut crystal in the following manner. 1*

The three-dimensional reciprocal lattice of thecrystal is constructed. N spheres each of radius l/x "(A is a characteristic wave-length of the jth element, i=1, 2 m), are constructed with a common point of tan-f gency. The common point of tangency of theN spheres. is made to coincide with the origin of thereciprooal lat- With the reciprocal lattice fixedin space, the line of centers of the spheres is rotated about any linedrawn When each'am'd every sphere intersects, or nearly intersects one reciprocal lattice point of a zone in the reciprocal lattice v(the zone fraction for the focussing case is satisfied; all planes (hkl) represented by reciprocal lattice points on the circles of reflection are respectively in reflecting positions for the-wavelengths characterized respectively by the spheres (of which the circles are traces); the direction of the line of centers of the spheres is the direction of the incident beam relative to the orientation of the reciprocal lattice. The direction of radii drawn to the reciprocal lattice points lying on the circles define the directions in which the detectors must point relative to the incident beam to receive the diflracted rays.

In this embodiment, crystal 6 has been bent to diffract wand reflect the characteristic radiations of Mo, Sn, Cr, Ni, and Cu. If the specimen contains any, or all of these elements, the crystal diffracts and reflects the characteristic radiations of each of the detectors separately. In addition, crystal 6 has been ground to converge the characteristic radiations at points on the fiocussing circle at which the detectors can be located for receiving a maximum amount of radiation with the smallest receiving slit. An exception has been made in this case for the detector of molybdenum radiation 8 which, because 50f the exaggerated size of the crystal shown, cannot be located at the focus 13 of the molybdenum characteristic radiation but is positioned to receive a diverging cone of rad ation.

As in the case described in the copending application, the choice of reciprocal lattice points is not restricted to the zone. For those points not in the zone the focussing properties will be somewhat sacrificed.

In FIG. 2, the specimen, again located on the focussing circle, is exposed to a beam of electrons produced by cathode 13, and focussed by electron lens system 14, and emits characteristic X-rays of each of the elements in the specimen. X-rays corresponding to some of the elements are diffracted and transmitted by the crystal 6, the remainder being reflected and fiocussed at :points on the 'focussing circle. For those X-rays which are reflected and fiocussed, the detector is positioned on the focussing circle as described in connection with FIG. 1. In the illustrated embodiment, characteristic X-rays of copper 181'6 reflected and focussed at a detector 12 located on the focussing circle.

X-rays of some Wave-lengths will not be reflected but will be transmitted through the crystal and will appear to be diverging from a point source on the focussing circle. In this case, the detector is positioned to intercept transmitted X-rays diverging from a virtual focus on the focussirtg circle. Such is the case for molybdenum radiation for which detector 8 is positioned behind the crystal and intercepts diffracted X-rays appearing to diverge from the virtual focus 15. To detect substantially only the X-rays diverging from this virtual focus, a converging Soller slit assembly 16 is interposed between the detector and the crystal. Also, in this case, a large a1 erture detector is employed.

While We have thus described our invention with a specific embodiment, other modifications will be apparent without departing from the spirit and scope of the invention as defined in the appended claims.

What we claim is:

1. An X-ray spectrograph for determining the constituent element of a material comprising means to excite a specimen of the material to produce characteristic X-rays, a plurality of detectors, and a stationary focussing diffracting crystal positioned to intercept and ditfract the characteristic X-rays emanating from said specimen, said crystal being deformed to diffract and focus radiation of each of a plurality of wave-lengths to one of a plurality of reciprocal lattice points of the crystal, and a plurality of detectors each of which is located at a reciprocal lattice point on the focussing circle of said crystal.

2. An X-ray spectrograph for determining the constituent elements of a material comprising means to excite a specimen of the material to produce characteristic X- rays, a plurality of detectors, and -a stationary tocussing diifracting crystal positioned to intercept and reflect characteristic X-rays of one wave-length and to transmit characteristic X-rays of another wave-length, said crystal being deformed to diflfract and focus each of said wave lengths to one of a plurality of reciprocal lattice points of the crystal, and a plurality of detectors each of which is located at a reciprocal lattice point on the focussing circle of said crystal.

3. An Y-ray spectrograph for determining the constituent elements of a material comprising means to excite a specimen of the material to produce characteristic Y- rays, a plurality of detectors, and a stationary focussing ditlracting crystal positioned to intercept and reflect characteristic X-rays of a plurality of wave-lengths, said crystal being deformed to reflect and focus X-rays of each of said wave-lengths to one of a plurality of reciprocal lattice points of the crystal, and a plurality of detectors each of which is located at a reciprocal lattice point on the focussing circle of said crystal.

4. An X-ray spectorgraph for determining the constituent elements of a material comprising means to excite a specimen of the material to produce characteristic X- rays, a plurality of detectors, and a stationary focussing diffracting crystal positioned to intercept and transmit characteristic X-rays of a plurality of wave-lengths, said crystal being deformed to transmit and focus X-rays of each of said Wave-lengths to one of a plurality of reciprocal lattice points of the crystal, and a plurality of detectors each of which is located at a reciprocal lattice point on the cfocussing circle of said crystal.

5. An X-ray spectrograph for determining the constituent elements of a material comprising a source of X-rays, means to expose a specimen of said material to said Xrays to produce fluorescent characteristic X-rays therefrom, a plurality of detectors, and a stationary focussing diffracting crystal positioned to intercept and diffract the characteristic X-rays from said specimen, said crystal being deformed to dilfract and focus X-radiation of each of a plurality of wave-lengths to one of a plurality of reciprocal lattice points of the crystal, and a plurality of detectors each of which is located at a reciprocal lattice point on the focussing circle or said crystal.

6. An X-ray spectrograph for determining the constituent elements of a material comprising a source of electrons, means to expose a specimen of said material to said electrons to produce characteristic X-rays therefrom, a plurality of detectors, and a stationary focussing diffracting crystal positioned to intercept and ditfract the characteristic X-rays from said specimen, said crystal being deformed to difliract and focus X-radiation of each of a plurality of wavelengths to one of a plurality of reciprocal lattice points of the crystal, and a plurality of detectors each of which is located at a reciprocal lattice point on the focussing circle of said crystal.

References Cited in the file of this patent UNITED STATES PATENTS 2,819,405 Bond Jan. 7, 1958 2,835,820 Birks May 20, 1958 2,837,655 Lang June 3, 1958 2,842,670 Birks July 8, 1958 2,897,367 Andermann et a1 July 28, 1959 2,897,371 Hasler July 28, 1959 2,928,944 Reiflel Mar. 15, 1960 2,928,945 Arndt et al Mar. 15, 1960 

1. AN X-RAY SPECTROGRAPH FOR DETERMINING THE CONSTITUENT ELEMENT OF A MATERIAL COMPRISING MEANS TO EXCITE A SPECIMEN OF THE MATERIAL TO PRODUCE CHARACTERISTIC X-RAYS, A PLURALITY OF DETECTORS, AND A STATIONARY FOCUSSING DIFFRACTING CRYSTAL POSITIONED TO INTERCEPT AND DIFFRACT THE CHARACTERISTIC X-RAYS EMANATING FROM SAID SPECIMEN, SAID CRYSTAL BEING DEFORMED TO DIFFRACT AND FOCUS RADIATION OF EACH OF A PLURALITY OF WAVE-LENGTHS TO ONE OF A PLURALITY OF RECIPROCAL LATTICE POINTS OF THE CRYSTAL, AND A PLURALITY OF DETECTORS EACH OF WHICH IS LOCATED AT A RECIPROCAL LATTICE POINT ON THE FOCUSSING CIRCLE OF SAID CRYSTAL. 